By details I meant the steps you have followed with their outcome and a description of the current state.
If the Microsoft Cleanup tool is freezing, try running it in safe mode. Someone suggested using CCleaner but I personally have not used it and I cannot advise. The idea is that you cannot uninstall the old version using its own uninstaller (which is the case for version 4.4.3 on Windows 7 x64) to use other tools to remove it from the Windows programs and Features. This should allow you to install the new version on top of the old one.
Just in case, reboot your system and then follow these steps:
1. Try to uninstall from Programs and Features (in case 4.5.0 is installed)
2. Use MSI Clean tool (try safe mode if you experience issues with it)
3. Follow instructions from this post: http://forums.eeye.com/forums/p/1155/5108.aspx#5108
Yesterday we have released the 4.5.1 release (not BETA) with support for Windows 7 x64. Download here: http://download.eeye.com/blinkpersonal